I need to create a local media server that can serve video content to hundreds (300-450) learners at a time. There will be no Internet connection; only a local Wi-Fi network the learners will connect to with their own tablets and mobile phones.
I am trying to find out if this is possible, where the bottlenecks in the systems would be, and what would be required to overcome them.
If anyone has any advice, I would be very grateful.
The biggest bottleneck I'd be worried about is Wi-Fi airtime (not bandwidth, but airtime per channel/AP).
Let's say a good proportion of your learners have tablets or phones that only do single-stream 802.11n Wi-Fi in 2.4GHz. With 20MHz-wide channels, that's a max of 72.2Mbps assuming the client is close to the AP. If the client is farther away, it could be as low as 1Mbps. But let's be generous and say they're all close enough to the APs to get the full 72.2Mbps PHY rate. The rule of thumb for TCP/IPv4 throughput over 802.11n Wi-Fi is that you get throughput around 70% of the PHY rate. That's 50Mbps of bandwidth per AP. Do you know the bitrate of the video content you'll be serving? If not, let's say is decent-quality (not overcompressed) HD at 5Mbps of H.264. That means you can only support 10 clients per AP. If this was a typical classroom environment with 20-30 students per room, you'd have to put in 2-3 APs per room. And then your traffic from one room would interfere with your traffic from another room, so you'd have to be sure to limit the transmit power of your APs. Pick your APs wisely, because consumer products don't always let you tweak the power effectively. You'd also want APs that can do load balancing to help make sure that your clients spread themselves evenly across the available APs. If you don't have classroom walls attenuating your signal, like if this is 300-450 people in a big hotel ballroom/convention hall/auditorium/sanctuary/gymnasium/theater/lecture hall, you might have a hard time providing enough Wi-Fi bandwidth density without becoming your own biggest source of interference.
Let's see what the best-case scenario might be. Let's say they all have iPhone 6s's with 2-stream 802.11ac (867Mbps max PHY rate with 80MHz-wide channels), and you have the APs to match. In some regions of the world, you're allowed to use up to 5 different 80MHz-wide channels in the 5GHz band. That works out to about 3Gbps of usable throughput before having to reuse channels. Let's also say you're cool with 1Mbps (360p or 480p) video. That could support 3,000 learners.
Note also that you could have bottlenecks at the server. If all this video is stored on HDDs (RAIDs, etc), there could be a lot of seeking back and forth to keep all those streams fed. You might want to store all this video on SSDs or otherwise consider your storage architecture. Also, if you had a single video server with a single Gigabit Ethernet as its connection to the network, it would only be able to give about 2Mbps to each of 450 clients, so you'd need to make sure your video bitrate is 2Mbps or less, or plan for using multiple video servers, or multiple GigE cards, or 10GigE, or something. You can probably find resources on properly sizing a video server elsewhere.
Please note that I've been assuming all the learners watching prerecorded, pre-encoded, stored content, with H.264-ish compression ratios. If this is live content, or if you were hoping to multicast the same video stream out to everyone at the same time, or if you wanted to have two-way video chats, or if you had to deal with old MPEG2 video, the calculations would be MUCH different.
